Leveraging Ethnic Backgrounds to Improve Collection of Race, Ethnicity, and Language Data.

INTRODUCTION: Healthcare disparities may be exacerbated by upstream incapacity to collect high-quality and accurate race, ethnicity, and language (REaL) data. There are opportunities to remedy these data barriers. We present the Denver Health (DH) REaL initiative, which was implemented in 2021. METHODS: Denver Health is a large safety net health system. After assessing the state of REaL data at DH, we developed a standard script, implemented training, and adapted our electronic health record to collect this information starting with an individual's ethnic background followed by questions on race, ethnicity, and preferred language. We analyzed the data for completeness after REaL implementation. RESULTS: A total of 207,490 patients who had at least one in-person registration encounter before and after the DH REaL implementation were included in our analysis. There was a significant decline in missing values for race (7.9%-0.5%, p < .001) and for ethnicity (7.6%-0.3%, p < .001) after implementation. Completely of language data also improved (3%-1.6%, p < .001). A year after our implementation, we knew over 99% of our cohort's self-identified race and ethnicity. CONCLUSIONS: Our initiative significantly reduced missing data by successfully leveraging ethnic background as the starting point of our REaL data collection.

Repurposing of the multiciliation gene regulatory network in fate specification of Cajal-Retzius neurons.

Cajal-Retzius cells (CRs) are key players in cerebral cortex development, and they display a unique transcriptomic identity. Here, we use scRNA-seq to reconstruct the differentiation trajectory of mouse hem-derived CRs, and we unravel the transient expression of a complete gene module previously known to control multiciliogenesis. However, CRs do not undergo centriole amplification or multiciliation. Upon deletion of Gmnc, the master regulator of multiciliogenesis, CRs are initially produced but fail to reach their normal identity resulting in their massive apoptosis. We further dissect the contribution of multiciliation effector genes and identify Trp73 as a key determinant. Finally, we use in utero electroporation to demonstrate that the intrinsic competence of hem progenitors as well as the heterochronic expression of Gmnc prevent centriole amplification in the CR lineage. Our work exemplifies how the co-option of a complete gene module, repurposed to control a distinct process, may contribute to the emergence of novel cell identities.

p73 is required for vessel integrity controlling endothelial junctional dynamics through Angiomotin.

Preservation of blood vessel integrity, which is critical for normal physiology and organ function, is controlled at multiple levels, including endothelial junctions. However, the mechanism that controls the adequate assembly of endothelial cell junctions is not fully defined. Here, we uncover TAp73 transcription factor as a vascular architect that orchestrates transcriptional programs involved in cell junction establishment and developmental blood vessel morphogenesis and identify Angiomotin (AMOT) as a TAp73 direct transcriptional target. Knockdown of p73 in endothelial cells not only results in decreased Angiomotin expression and localization at intercellular junctions, but also affects its downstream function regarding Yes-associated protein (YAP) cytoplasmic sequestration upon cell-cell contact. Analysis of adherens junctional morphology after p73-knockdown in human endothelial cells revealed striking alterations, particularly a sharp increase in serrated junctions and actin bundles appearing as stress fibers, both features associated with enhanced barrier permeability. In turn, stabilization of Angiomotin levels rescued those junctional defects, confirming that TAp73 controls endothelial junction dynamics, at least in part, through the regulation of Angiomotin. The observed defects in monolayer integrity were linked to hyperpermeability and reduced transendothelial electric resistance. Moreover, p73-knockout retinas showed a defective sprout morphology coupled with hemorrhages, highlighting the physiological relevance of p73 regulation in the maintenance of vessel integrity in vivo. We propose a new model in which TAp73 acts as a vascular architect integrating transcriptional programs that will impinge with Angiomotin/YAP signaling to maintain junctional dynamics and integrity, while balancing endothelial cell rearrangements in angiogenic vessels.

p73 as a Tissue Architect.

The TP73 gene belongs to the p53 family comprised by p53, p63, and p73. In response to physiological and pathological signals these transcription factors regulate multiple molecular pathways which merge in an ensemble of interconnected networks, in which the control of cell proliferation and cell death occupies a prominent position. However, the complex phenotype of the Trp73 deficient mice has revealed that the biological relevance of this gene does not exclusively rely on its growth suppression effects, but it is also intertwined with other fundamental roles governing different aspects of tissue physiology. p73 function is essential for the organization and homeostasis of different complex microenvironments, like the neurogenic niche, which supports the neural progenitor cells and the ependyma, the male and female reproductive organs, the respiratory epithelium or the vascular network. We propose that all these, apparently unrelated, developmental roles, have a common denominator: p73 function as a tissue architect. Tissue architecture is defined by the nature and the integrity of its cellular and extracellular compartments, and it is based on proper adhesive cell-cell and cell-extracellular matrix interactions as well as the establishment of cellular polarity. In this work, we will review the current understanding of p73 role as a neurogenic niche architect through the regulation of cell adhesion, cytoskeleton dynamics and Planar Cell Polarity, and give a general overview of TAp73 as a hub modulator of these functions, whose alteration could impinge in many of the Trp73 -/- phenotypes.

Deciphering the Nature of Trp73 Isoforms in Mouse Embryonic Stem Cell Models: Generation of Isoform-Specific Deficient Cell Lines Using the CRISPR/Cas9 Gene Editing System.

The p53 family has been widely studied for its role in various physiological and pathological processes. Imbalance of p53 family proteins may contribute to developmental abnormalities and pathologies in humans. This family exerts its functions through a profusion of isoforms that are generated by different promoter usage and alternative splicing in a cell type dependent manner. In particular, the Trp73 gene gives rise to TA and DN-p73 isoforms that confer p73 a dual nature. The biological relevance of p73 does not only rely on its tumor suppression effects, but on its pivotal role in several developmental processes. Therefore, the generation of cellular models that allow the study of the individual isoforms in a physiological context is of great biomedical relevance. We generated specific TA and DN-p73-deficient mouse embryonic stem cell lines using the CRISPR/Cas9 gene editing system and validated them as physiological bona fide p73-isoform knockout models. Global gene expression analysis revealed isoform-specific alterations of distinctive transcriptional networks. Elimination of TA or DN-p73 is compatible with pluripotency but prompts naïve pluripotent stem cell transition into the primed state, compromising adequate lineage differentiation, thus suggesting that differential expression of p73 isoforms acts as a rheostat during early cell fate determination.

Hypoxia compensates cell cycle arrest with progenitor differentiation during angiogenesis.

Angiogenesis, the main mechanism that allows vascular expansion for tissue regeneration or disease progression, is often triggered by an imbalance between oxygen consumption and demand. Here, by analyzing changes in the transcriptomic profile of endothelial cells (ECs) under hypoxia we uncovered that the repression of cell cycle entry and DNA replication stand as central responses in the early adaptation of ECs to low oxygen tension. Accordingly, hypoxia imposed a restriction in S-phase in ECs that is mediated by Hypoxia-Inducible Factors. Our results indicate that the induction of angiogenesis by hypoxia in Embryoid Bodies generated from murine Stem Cells is accomplished by the compensation of decreased S-phase entry in mature ECs and differentiation of progenitor cells. This conditioning most likely allows an optimum remodeling of the vascular network. Identification of the molecular underpinnings of cell cycle arrest by hypoxia would be relevant for the design of improved strategies aimed to suppress angiogenesis in pathological contexts where hypoxia is a driver of neovascularization.

The Trp73 Mutant Mice: A Ciliopathy Model That Uncouples Ciliogenesis From Planar Cell Polarity.

p73 transcription factor belongs to one of the most important gene families in vertebrate biology, the p53-family. Trp73 gene, like the other family members, generates multiple isoforms named TA and DNp73, with different and, sometimes, antagonist functions. Although p73 shares many biological functions with p53, it also plays distinct roles during development. Trp73 null mice (p73KO from now on) show multiple phenotypes as gastrointestinal and cranial hemorrhages, rhinitis and severe central nervous system defects. Several groups, including ours, have revisited the apparently unrelated phenotypes observed in total p73KO and revealed a novel p73 function in the organization of ciliated epithelia in brain and trachea, but also an essential role as regulator of ependymal planar cell polarity. Unlike p73KO or TAp73KO mice, tumor-prone Trp53-/- mice (p53KO) do not present ependymal ciliary or planar cell polarity defects, indicating that regulation of ciliogenesis and PCP is a p73-specific function. Thus, loss of ciliary biogenesis and epithelial organization might be a common underlying cause of the diverse p73KO-phenotypes, highlighting Trp73 role as an architect of the epithelial tissue. In this review we would like to discuss the data regarding p73 role as regulator of ependymal cell ciliogenesis and PCP, supporting the view of the Trp73-mutant mice as a model that uncouples ciliogenesis from PCP and a possible model of human congenital hydrocephalus.

p73 regulates ependymal planar cell polarity by modulating actin and microtubule cytoskeleton.

Planar cell polarity (PCP) and intercellular junctional complexes establish tissue structure and coordinated behaviors across epithelial sheets. In multiciliated ependymal cells, rotational and translational PCP coordinate cilia beating and direct cerebrospinal fluid circulation. Thus, PCP disruption results in ciliopathies and hydrocephalus. PCP establishment depends on the polarization of cytoskeleton and requires the asymmetric localization of core and global regulatory modules, including membrane proteins like Vangl1/2 or Frizzled. We analyzed the subcellular localization of select proteins that make up these modules in ependymal cells and the effect of Trp73 loss on their localization. We identify a novel function of the Trp73 tumor suppressor gene, the TAp73 isoform in particular, as an essential regulator of PCP through the modulation of actin and microtubule cytoskeleton dynamics, demonstrating that Trp73 is a key player in the organization of ependymal ciliated epithelia. Mechanistically, we show that p73 regulates translational PCP and actin dynamics through TAp73-dependent modulation of non-musclemyosin-II activity. In addition, TAp73 is required for the asymmetric localization of PCP-core and global signaling modules and regulates polarized microtubule dynamics, which in turn set up the rotational PCP. Therefore, TAp73 modulates, directly and/or indirectly, transcriptional programs regulating actin and microtubules dynamics and Golgi organization signaling pathways. These results shed light into the mechanism of ependymal cell planar polarization and reveal p73 as an epithelial architect during development regulating the cellular cytoskeleton.

p73 is required for appropriate BMP-induced mesenchymal-to-epithelial transition during somatic cell reprogramming.

The generation of induced pluripotent stem cells (iPSCs) by somatic cell reprogramming holds great potential for modeling human diseases. However, the reprogramming process remains very inefficient and a better understanding of its basic biology is required. The mesenchymal-to-epithelial transition (MET) has been recognized as a crucial step for the successful reprogramming of fibroblasts into iPSCs. It has been reported that the p53 tumor suppressor gene acts as a barrier of this process, while its homolog p63 acts as an enabling factor. In this regard, the information concerning the role of the third homolog, p73, during cell reprogramming is limited. Here, we derive total Trp73 knockout mouse embryonic fibroblasts, with or without Trp53, and examine their reprogramming capacity. We show that p73 is required for effective reprogramming by the Yamanaka factors, even in the absence of p53. Lack of p73 affects the early stages of reprogramming, impairing the MET and resulting in altered maturation and stabilization phases. Accordingly, the obtained p73-deficient iPSCs have a defective epithelial phenotype and alterations in the expression of pluripotency markers. We demonstrate that p73 deficiency impairs the MET, at least in part, by hindering BMP pathway activation. We report that p73 is a positive modulator of the BMP circuit, enhancing its activation by DNp73 repression of the Smad6 promoter. Collectively, these findings provide mechanistic insight into the MET process, proposing p73 as an enhancer of MET during cellular reprogramming.

Expression of the Parkinson's Disease-Associated Gene Alpha-Synuclein is Regulated by the Neuronal Cell Fate Determinant TRIM32.

Alpha-synuclein is an abundant neuronal protein which has been associated with physiological processes like synaptic function, neurogenesis, and neuronal differentiation but also with pathological neurodegeneration. Indeed, alpha-synuclein (snca) is one of the major genes implicated in Parkinson's disease (PD). However, little is known about the regulation of alpha-synuclein expression. Unveiling the mechanisms that control its regulation is of high importance, as it will enable to further investigate and comprehend the physiological role of alpha-synuclein as well as its potential contribution in the aetiology of PD. Previously, we have shown that the protein TRIM32 regulates fate specification of neural stem cells. Here, we investigated the impact of TRIM32 on snca expression regulation in vitro and in vivo in neural stem cells and neurons. We demonstrated that TRIM32 is positively influencing snca expression in a neuronal cell line, while the absence of TRIM32 is causing deregulated levels of snca transcripts. Finally, we provided evidence that TRIM32 binds to the promoter region of snca, suggesting a novel mechanism of its transcriptional regulation. On the one hand, the presented data link the PD-associated gene alpha-synuclein to the neuronal cell fate determinant TRIM32 and thereby support the concept that PD is a neurodevelopmental disorder. On the other hand, they imply that defects in olfactory bulb adult neurogenesis might contribute to early PD-associated non-motor symptoms like hyposmia.

Novel role of p73 as a regulator of developmental angiogenesis: Implication for cancer therapy.

Information regarding the role of p73 in the regulation of angiogenesis has been incomplete and quite controversial. Remarkably, several groups, including ours, have recently demonstrated that TP73 plays a fundamental role in angiogenesis regulation and that differential expression of TP73 could have important consequences in tumor angiogenesis. Here, we discuss a possible model for p73 function in the regulation of developmental angiogenesis and tumor angiogenesis.

p73 is required for ependymal cell maturation and neurogenic SVZ cytoarchitecture.

The adult subventricular zone (SVZ) is a highly organized microenvironment established during the first postnatal days when radial glia cells begin to transform into type B-cells and ependymal cells, all of which will form regenerative units, pinwheels, along the lateral wall of the lateral ventricle. Here, we identify p73, a p53 homologue, as a critical factor controlling both cell-type specification and structural organization of the developing mouse SVZ. We describe that p73 deficiency halts the transition of the radial glia into ependymal cells, leading to the emergence of immature cells with abnormal identities in the ventricle and resulting in loss of the ventricular integrity. p73-deficient ependymal cells have noticeably impaired ciliogenesis and they fail to organize into pinwheels, disrupting SVZ niche structure and function. Therefore, p73 is essential for appropriate ependymal cell maturation and the establishment of the neurogenic niche architecture. Accordingly, lack of p73 results in impaired neurogenesis. Moreover, p73 is required for translational planar cell polarity establishment, since p73 deficiency results in profound defects in cilia organization in individual cells and in intercellular patch orientation. Thus, our data reveal a completely new function of p73, independent of p53, in the neurogenic architecture of the SVZ of rodent brain and in the establishment of ependymal planar cell polarity with important implications in neurogenesis. © 2015 Wiley Periodicals, Inc. Develop Neurobiol 76: 730-747, 2016.

The mitochondrial complex I activity is reduced in cells with impaired cystic fibrosis transmembrane conductance regulator (CFTR) function.

Cystic fibrosis (CF) is a frequent and lethal autosomal recessive disease. It results from different possible mutations in the CFTR gene, which encodes the CFTR chloride channel. We have previously studied the differential expression of genes in CF and CF corrected cell lines, and found a reduced expression of MTND4 in CF cells. MTND4 is a mitochondrial gene encoding the MTND4 subunit of the mitochondrial Complex I (mCx-I). Since this subunit is essential for the assembly and activity of mCx-I, we have now studied whether the activity of this complex was also affected in CF cells. By using Blue Native-PAGE, the in-gel activity (IGA) of the mCx-I was found reduced in CFDE and IB3-1 cells (CF cell lines) compared with CFDE/6RepCFTR and S9 cells, respectively (CFDE and IB3-1 cells ectopically expressing wild-type CFTR). Moreover, colon carcinoma T84 and Caco-2 cells, which express wt-CFTR, either treated with CFTR inhibitors (glibenclamide, CFTR(inh)-172 or GlyH101) or transfected with a CFTR-specific shRNAi, showed a significant reduction on the IGA of mCx-I. The reduction of the mCx-I activity caused by CFTR inhibition under physiological or pathological conditions may have a profound impact on mitochondrial functions of CF and non-CF cells.

Measurement of cystic fibrosis transmembrane conductance regulator activity using fluorescence spectrophotometry.

Cystic fibrosis (CF) is a frequent autosomal recessive disease caused by mutations that impair the CF transmembrane conductance regulator (CFTR) protein function. CFTR is a chloride channel activated by cyclic AMP (cAMP) via protein kinase A (PKA) and ATP hydrolysis. We describe here a method to measure CFTR activity in a monolayer of cultured cells using a fluorescence spectrophotometer and the chloride-sensitive probe 6-methoxy-N-(3-sulfopropyl)quinolinium (SPQ). Modifying a slice holder, the spectrophotometer quartz cuvette was converted in a perfusion chamber, allowing measurement of CFTR activity in real time, in a monolayer of T84 colon carcinoma cells. The SPQ Stern-Volmer constant (K(Cl(-))) for chloride in water solution was 115.0 ± 2.8M(-1), whereas the intracellular (K(Cl(-))) was 17.8 ± 0.8 M(-1), for T84 cells. A functional analysis was performed by measuring CFTR activity in T84 cells. The CFTR transport inhibitors CFTR(inh)-172 (5 µM) and glibenclamide (100 µM) showed a significant reduction (P<0.05) in CFTR activity. This simple method allows measuring CFTR activity in a very simple, reproducible, and sensitive way.

[Fatty acid composition of human milk from mothers of preterm and full-term infants]. / Composición en ácidos grasos de leche de madres de recién nacidos de pretérmino y de término.

INTRODUCTION: Human milk is an essential food for newborns and affects life in the long or short terms. Its composition is modified by nutritional status and maternal diet as well as by gestational age of the newborn. It provides human milk-fed infants with the medium-chain fatty acids which are a source of energy, and essential fatty acids and their metabolic derivatives which have been involved in the neural maturation. OBJECTIVES: Due to the fact that there is little local data concerning the fatty acid composition in human milk of pre-term and full-term newborns, the present study was carried out in women living in the urban area of the Buenos Aires Province. MATERIALS AND METHODS: Samples were provided by the Bank of Human Milk, H.I.G.A. San Martín Hospital. They corresponded to mothers who had delivered preterm infants (28-36 weeks of gestational age) or full-term infants (37-42 weeks of gestational ages). Total lipids were extracted, and the fatty acid composition was determined by gas-liquid chromatography. RESULTS: Results showed increases in saturated fatty acids up to 14 carbon atoms and in polyunsaturated fatty acids in mothers of preterm newborns compared with those of full-term newborns. CONCLUSIONS: It can be concluded that gestational age affects human milk fatty acid composition. This food is essential for pre-term newborns as it is the source of energetic compounds (saturated fatty acids) as well as plastic compounds, (polyunsaturated fatty acids) which are essential for the synthesis of structural lipids and neural development.

Composición en ácidos grasos de leche de madres de recién nacidos de pretérminoy de término / Fatty acid composition of human milk from mothers of preterm and full-term infants

Introducción. La leche materna es un alimento esencial para el recién nacido e influye en su calidad de vida en el corto y largo plazo. Su composición se modifica con el estado nutricional,la dieta materna y la edad gestacional del recién nacido. Entre otros nutrientes fundamentales provee a los lactantes de ácidos grasos de cadena media de fácil utilización, y de ácidos grasosesenciales y sus derivados metabólicos, en especial ácidos araquidónico y docosahexaenoico, que han sido involucrados en la maduración neural.Objetivos. Dada la escasez de datos locales se consideró la importancia de estudiar la composición en ácidos grasos de la leche de madres de reciénnacidos de pretérmino y de término en mujeres del área urbana de la Provincia de Buenos Aires.Material y métodos. Las muestras fueron obtenidas del Banco de Leche Materna H.I.G.A San Martín. Se extrajeron los lípidos totales y se determinó la composición en ácidos grasos porcromatografía de gas-líquido.Resultados. Los resultados muestran aumentos en ácidos grasos saturados de hasta 14 átomos de carbono y en los ácidos grasos poliinsaturadosen la leche de madres de recién nacidos de pretérmino con respecto a la de madres de recién nacidos de término.Conclusiones. La edad gestacional influye en la composición de los ácidos grasos de la leche materna, siendo la leche de madres de lactantesprematuros una fuente imprescindible de elementos energéticos (ácidos grasos saturados) y de elementos plásticos (ácidos grasos poliinsaturados)fundamentales para la síntesis de lípidosestructurales y en el desarrollo neural.

Composición en ácidos grasos de leche de madres de recién nacidos de pretérminoy de término / Fatty acid composition of human milk from mothers of preterm and full-term infants

Introducción. La leche materna es un alimento esencial para el recién nacido e influye en su calidad de vida en el corto y largo plazo. Su composición se modifica con el estado nutricional,la dieta materna y la edad gestacional del recién nacido. Entre otros nutrientes fundamentales provee a los lactantes de ácidos grasos de cadena media de fácil utilización, y de ácidos grasosesenciales y sus derivados metabólicos, en especial ácidos araquidónico y docosahexaenoico, que han sido involucrados en la maduración neural.Objetivos. Dada la escasez de datos locales se consideró la importancia de estudiar la composición en ácidos grasos de la leche de madres de reciénnacidos de pretérmino y de término en mujeres del área urbana de la Provincia de Buenos Aires.Material y métodos. Las muestras fueron obtenidas del Banco de Leche Materna H.I.G.A San Martín. Se extrajeron los lípidos totales y se determinó la composición en ácidos grasos porcromatografía de gas-líquido.Resultados. Los resultados muestran aumentos en ácidos grasos saturados de hasta 14 átomos de carbono y en los ácidos grasos poliinsaturadosen la leche de madres de recién nacidos de pretérmino con respecto a la de madres de recién nacidos de término.Conclusiones. La edad gestacional influye en la composición de los ácidos grasos de la leche materna, siendo la leche de madres de lactantesprematuros una fuente imprescindible de elementos energéticos (ácidos grasos saturados) y de elementos plásticos (ácidos grasos poliinsaturados)fundamentales para la síntesis de lípidosestructurales y en el desarrollo neural.(AU)

p73 plays a role in erythroid differentiation through GATA1 induction.

The TP73 gene gives rise to transactivation domain-p73 isoforms (TAp73) as well as DeltaNp73 variants with a truncated N terminus. Although TAp73alpha and -beta proteins are capable of inducing cell cycle arrest, apoptosis, and differentiation, DeltaNp73 acts in many cell types as a dominant-negative repressor of p53 and TAp73. It has been proposed that p73 is involved in myeloid differentiation, and its altered expression is involved in leukemic degeneration. However, there is little evidence as to which p73 variants (TA or DeltaN) are expressed during differentiation and whether specific p73 isoforms have the capacity to induce, or hinder, this differentiation in leukemia cells. In this study we identify GATA1 as a direct transcriptional target of TAp73alpha. Furthermore, TAp73alpha induces GATA1 activity, and it is required for erythroid differentiation. Additionally, we describe a functional cooperation between TAp73 and DeltaNp73 in the context of erythroid differentiation in human myeloid cells, K562 and UT-7. Moreover, the impaired expression of GATA1 and other erythroid genes in the liver of p73KO embryos, together with the moderated anemia observed in p73KO young mice, suggests a physiological role for TP73 in erythropoiesis.

Immediate upregulation of proteins belonging to different branches of the apoptotic cascade in the retina after optic nerve transection and optic nerve crush.

PURPOSE: To further investigate the molecular signals underlying optic nerve (ON) injury, the authors analyzed in adult control, ON-transected, and ON-crushed retinas the expression pattern and time-course regulation of the following proteins, all of which are linked to apoptosis through different pathways: Stat 1, caspase 11 (inflammation and death), cathepsins C and B (lysosomal death pathway), calpain 1 (endoplasmic reticulum stress), calreticulin (apoptosis marker), Jun (early response), and aryl hydrocarbon receptor (cell cycle arrest). METHODS: Adult female rats were subjected to intraorbital optic nerve transection (IONT) or intraorbital optic nerve crush (IONC). Protein from naive and ON-injured adult rat retinas was extracted at different times postlesion, and Western blotting experiments were performed. For immunohistofluorescence analyses, retinal ganglion cells (RGCs) were retrogradely identified with fluorogold applied to the superior colliculi 1 week before injury. RESULTS: Western blotting analyses revealed upregulation of all the analyzed proteins as early as 12 hours postlesion (hpl), peaking at 48 hpl, in agreement with our previous RNA study findings. Furthermore, immunohistofluorescence to radial sections showed that all but Stat 1 were expressed by the primarily injured neurons, the RGCs, as seen by colocalization with fluorogold. CONCLUSIONS: All analyzed proteins were upregulated in the retina after IONT or IONC as early as 12 hpl, indicating that ON injury regulates several branches of the apoptotic cascade and suggesting that commitment to death might be an earlier event than previously anticipated.

c-Myc inhibits Ras-mediated differentiation of pheochromocytoma cells by blocking c-Jun up-regulation.

Although mutant Ras proteins were originally described as transforming oncoproteins, they induce growth arrest, senescence, and/or differentiation in many cell types. c-Myc is an oncogenic transcription factor that cooperates with Ras in cellular transformation and oncogenesis. However, the Myc-Ras relationship in cellular differentiation is largely unknown. Here, we have analyzed the effects of c-Myc on PC12-derived cells (UR61 cell line), harboring an inducible N-Ras oncogene. In these cells, Ras activation induces neuronal-like differentiation by a process involving c-Jun activation. We found that c-Myc inhibited Ras-mediated differentiation by a mechanism that involves the blockade of c-Jun induction in response to Ras signal. Accordingly, ectopically expressed c-Jun could bypass c-Myc impediment of Ras-induced differentiation and activator protein 1 activation. Interestingly, it did not rescue the proliferative arrest elicited by Ras and did not enhance the differentiation-associated apoptosis. The blockade of Ras-mediated induction of c-Jun takes place at the level of c-Jun proximal promoter. Mutational analysis revealed that c-Myc regions involved in DNA binding and transactivation are required to block differentiation and c-Jun induction. c-Myc does not seem to require Miz-1 to inhibit differentiation and block c-Jun induction. Furthermore, Max is not required for c-Myc activity, as UR61 cells lack a functional Max gene. c-Myc-inhibitory effect on the Ras/c-Jun connection is not restricted to UR61 cells as it can occur in other cell types as K562 or HEK293. In conclusion, we describe a novel interplay between c-Myc and c-Jun that controls the ability of Ras to trigger the differentiation program of pheochromocytoma cells.